The field of the invention is the manufacture of 2,6-dimethylmorpholine and the invention is particularly concerned with dehydrating 2,6-dimethylmorpholine. The product obtained is practically dry when 2,6-dimethylmorpholine is isolated or recovered from aqueous solutions.
The state of the art of separating mixtures of water/2,6-dimethylmorpholine may be ascertained by reference to U.S. Pat. No. 3,083,202; J. Org. Chem., Vol. 11 (1946), pp. 286-291; and Chemical Abstracts, Vol. 40, 4732, 1-7, the disclosures of which are incorporated herein by reference.
U.S. Pat. No. 3,083,202 discloses the use of azeotropic rectification with an entrainer such as benzene for the separation of mixtures of water/2,6-dimethylmorpholine. Liquid-liquid extraction, using for instance ether for the dehydration of alkylmorpholine, is disclosed in the J. Organic Chem. and Chemical Abstracts articles incorporated above.
According to the state of the art, water and 2,6-dimethylmorpholine cannot be separated by simple rectification because they are fully miscible and form an azeotrope (70% by weight of water, b.p. 99.6.degree. C.; Azeotropic data 111, System #567).
The entrainer rectification for drying liquids completely miscible with water is commercially available. However, it incurs the following drawbacks:
An additional column is required as a waste-water stripper because ecologically no water saturated with entrainer may be discharged into the environment. Introducing an accessory substance (entrainer) requires an additional supply storage with all the resulting drawbacks. Furthermore, there is the danger of contaminating the product with the accessory substance and also the problem of enriching by-products present in small amounts in the entrainer circuit, with the possibility of complications resulting from these enriched by-products. Again, there is the requirement to evaporate large amounts of entrainer and to condense them. Entrainer evaporation demands appreciable and additional energy.